The present invention relates to films of monolithic polymers, and, in particular, to embossed sheets of a monolithic polymer and methods of forming the same.
Films of monolithic polymers are films which transmit moisture vapor molecules, yet do not transmit liquids. Monolithic polymer films are distinct from "microporous films" in that no micropore exists in the monolithic polymer film. The monolithic polymer films have a chemical affinity to moisture vapor molecules. Moisture vapor molecules on one side of a monolithic polymer film are absorbed by the monolithic polymer. A gradient of moisture vapor content will exist in the monolithic polymer film with a high moisture content on the side of the monolithic polymer film adjacent to the water vapor, and a low moisture content on the opposite side of the monolithic polymer film. The attraction of the monolithic polymers to moisture vapor molecules will cause the low moisture content side of the film to attract moisture vapor molecules from the high moisture content side of the film. Moisture vapor molecules on the low moisture content side of the film will be transmitted to the atmosphere adjacent to the low moisture content side of the film. Moisture Vapor Transmission Rate (MVTR) is the rate that a film will transmit moisture vapor from one surface to another, and is usually expressed in terms of grams per square meter per day (g/m.sup.2 /day).
Monolithic polymer films are useful in many applications, such as medical applications where ASTM E-22 viral barrier requirements must be met. For example, in a medical application for a garment, the liquid impervious nature of the film is important to protect the wearer from body fluids of a patient which may bear pathogens. However, moisture vapor transmission is important to permit moisture vapor to escape from within the garment and keep the wearer of the garment comfortable. Therefore, it is desirable to have monolithic polymer films with a high MVTR.
Monolithic polymers are a block copolymer containing a hard or crystalline segment and a soft or amorphous segment. The crystalline segment is usually a component such as polybutylene terephthalate, or the like. The amorphous segment is usually a component similar to a component based upon long-chain polyester glycols, or the like. The MVTR properties of a monolithic polymer film are based upon the ratio of the crystalline segment to the amorphous segment. Generally, the greater the amount of amorphous segment per crystalline segment, the greater an MVTR that can be expected for the film.
The amorphous segment of a monolithic polymer film gives the film soft and tacky characteristics. The soft and tacky nature of a monolithic polymer film tends to cause the film to block when wound on a roll. As the proportion of the amorphous segment to the crystalline segment increases in a film, in order to increase the film MVTR, the film will have a greater susceptibility to blocking. To overcome blocking, conventional prior art has utilized a release liner between the layers of monolithic polymer films wound on a roll. The use of a release liner adds costs and handling difficulties in a manufacturing process. Therefore, there is a need for monolithic films with a lower tendency to block without reducing the proportion of the amorphous segment in the film.
Generally, the thinner a monolithic polymer film, the better the film will transmit moisture vapor molecules. However, as a film gets thinner, the film becomes more difficult for handling by manufacturing equipment and end users. Therefore, there is a need for monolithic polymer films that are thin but can easily be handled during manufacturing and by end users.